Mp-a and Mp-t Machines, Multipolar Machines for Alternating and Three-Phase Currents

ABSTRACT

A machine (FIG.  3 B) includes inner and outer stator ( 5  and  6 ) and a rotor ( 2 ) located therebetween. The rotor includes a wall with a constant thickness and an elongates S-ribbon ( 172 ) overlapping the gaps in the wall of the rotor.

CROSS-REFERENCE TO RELATED APPLICATIONS

Related U.S. patent applications are:

“Multipolar Machines—Optimized HomopolarMotors/Generators/Transformers,” D. Kuhlmann-Wilsdorf, patentapplication, filed Jul. 8, 2003, PCT Application PCT/US03/22248.

“Multipolar-Plus Machines—Multipolar Machines with Reduced Numbers ofBrushes,” D. Kuhlmann-Wilsdorf, patent application, filed ______, PCTApplication ______.

FIELD AND AIM OF THE INVENTION

The present invention expands the “multipolar machine” (MP machine)invention described in “Multipolar Machines—Optimized HomopolarMotors/Generators/Transformers,” D. Kuhlmann-Wilsdorf, filed Jul. 8,2003 and a follow-up invention described in “Multipolar-PlusMachines—Multipolar Machines with Reduced Numbers of Brushes” D.Kuhlmann-Wilsdorf. The present invention specifically seeks patentprotection for MP-machines that are adapted to alternating (AC) and/orthree-phase (3-phase) currents and are dubbed MP-A and MP-T machines,respectively, whereas MP and MP-Plus machines are adapted to DCcurrents.

Machines of the MP family share three basic construction features,including (A) a generally cylindrical rotor, that may be constituted ofa unitary rotor or a set of concentric, mechanically fused butelectrically insulated rotor layers, not necessarily of constantdiameter, which rotor is capable of carrying current in substantiallyaxial direction but not in substantially circumferential direction, (B)multiple magnetic field sources surrounding the rotor at the outside andinside such that they establish a magnetic flux density B in amultiplicity of axially extended zones in the wall of that rotor, whichmagnetic flux density alternates in radial orientation betweenneighboring zones; (C) means to direct a current to sequentially passthrough a multiplicity of the zones such that the Lorentz force has thesame, sense of rotation everywhere.

In line with the above general description, typically, MP and MP-Plusmachines comprise three concentric (rotationally symmetrical but notnecessarily simply cylindrical) tubes that are centered on a commonrotation axis. These are an outer and an inner magnet tube to which themagnetic field sources in the form of axially extended rows of permanentmagnets are fastened such that radially correlated opposing magnet polesface each other across a gap with alternating polarity in neighboringrows to form axially extended zones of strong radial magnetic flux, B,and a rotor or rotor set that is capable of flowing current in the zonesand of rotating relative to the rows of magnetic pole pairs in the gapbetween the inner and outer magnet tube.

As already indicated, the magnets in the magnet tubes are arranged so asto generate regularly spaced, axially extended “zones” that arepenetrated by radial magnetic flux density, B, whose sign alternatesfrom zone to zone, with flux-free gaps between the zones. Further,simple MP and MP-Plus machines comprise “current channeling” rotors thatpermit current flow only parallel to, but not normal to, the zones, andmeans to guide currents sequentially in “turns” through a plurality ofzones such that the current direction changes as the direction of Bchanges, to the effect that the rotational direction of the Lorentzforce on a current is the same over all successive “turns” of thecurrent.

In simple MP machines, the means for guiding a current sequentiallythrough a multiplicity of zones, are electrical brushes at each end of azone that slide on slip rings on the outer rotor surface and arepair-wise electrically connected. In MP-Plus machines a majority ofthese brushes are replaced by “flags” that connect equivalent points ofneighboring zones in neighboring rotors. In accord with the abovecharacteristics, simple MP as well as MP-Plus machines are homopolar,i.e. the current path in them remains stationary while operating themachine. This feature confers extremely low electronic noise levels,i.e. permits military “stealth” and therefore is highly prized in the USNavy, when the machines are operated with DC current in contrast torectified AC or three-phase current. In fact, simple MP and MP-Plusmachines may, in the electric motor mode, be operated not only withdirect current (DC), but also with rectified alternating current (AC)and/or three-phase current (3-Ph), but in the generator mode are capableof generating only DC current. They are therefore best described as“adapted” to DC.

The present invention retains the basic features labeled (A), (B) and(C) above but replaces metallic “current channeling” rotors with rotorscomprising lengthwise extended sections of elongated conductors, dubbed“S-ribbons,” that are continuous through a multiplicity of axiallyextended sections of a width and spacing coincident with those of thezones. Since on machine rotation, the resulting induced EMF's, i.e. whenconsecutive segments of S-ribbons pass through a number of neighboringzones, on through gaps and followed by passage to the next set ofneighboring zones, alternates, machines in accordance with the presentinvention are not homopolar but are “adapted to” AC with a singleS-ribbon or, by the use of three regular placed independent S-ribbons,are “adapted to” 3-phase current. Thus the present invention is based ona different rotor design than used in simple MP and MP-Plus machines.Even so, machines according to the present invention share the alreadylisted features (A) and (B) of MP machines and therefore belong to thefamily of multipolar (MP) electrical machines.

Accordingly, one aim of the present invention is to broaden the range ofMP machines to include AC-machines (MP-A machines) orthree-phase-current-machines. (MP-T machines). An important secondaryaim is to optionally eliminate the need for electrical brushes and sliprings which is done by rotating the magnet tubes instead of the rotor ashas been done with simple MP and MP-Plus machines.

I. GENERAL DESCRIPTION OF THE INVENTION

According to the present invention the first aim, already indicated, isto achieve machines of multipolar (MP) type that are AC and/or 3-phasecurrent machines, and that are controlled much like conventional AC andthree-phase machines. This aim is achieved by means of rotors thatcomprise at least one electrically conductive ribbon, dubbed an“S-ribbon,” shaped so that, in rotation, it periodically substantiallyoverlaps a multiplicity of adjoining zones, alternating withsubstantially overlapping gaps between the same adjoining zones. As aresult, when connected to an external power source or sink, S-ribbonsperiodically conduct current along multiple zones of high magnetic fluxand generate, or are subject to, Lorentz forces of same rotationaldirection along their whole length within the zones. On rotation, then,over much or most of their lengths, S-ribbons cycle between zones andgaps, wherein the Lorentz forces, and hence the machine torque,alternate between maximum clockwise to zero and maximum anticlockwise.

In addition, the second aim, namely MP machines that do not require anyelectric brushes, is achieved through reversing the relative motionbetween magnet tubes and rotors made as above, so that the two magnettubes spin with the machine axle (or at any rate if there should be nocentral axle relative to the stationary surroundings) and the rotor isstationary. Again, the relative motion between an S-ribbon and magnetscauses the Lorentz force to oscillate when any chosen point on the rotorpasses from one zone of magnetic flux between paired magnet polesthrough a gap to the next zone, i.e. which has the opposite direction ofmagnetic field.

MP machines as described and comprising a single S-ribbon may beoperated with, or in the generator mode will deliver, AC current andtherefore are dubbed MP-A machines as already noted. By molding twosimilar, regularly spaced S-ribbons into the rotor, the machine willgenerate two out-of-phase AC currents that may be used independent ofeach other. With three similar S-ribbons in the rotor, at ⅓ the spacingof neighboring zones of same polarity, a machine will generatethree-phase power in the generator mode and can be operated withthree-phase current in the motor mode. Such machines are dubbed MP-Tmachines. The speed as well as torque of MP-A and MP-T machines may becontrolled via inverters, i.e. via frequency instead of voltage andcurrent control as for MP and MP Plus machines.

Note that in the motor mode, both MP-A and MP-T machines can be drivenby means of chopped and inverted DC current. Neither MP-A not MP-Tmachines are homopolar, i.e. they will emit electrical noise. However,the electromagnetic noise level of MP-A as well as MP-T machines will bemodest (i) because the dipolar arrangement of the poles in the rotatingmagnet tubes causes the magnetic fields of MP-A and MP-T machines to beshort ranged, (ii) because the current direction in neighboring parallelsegments of the S-ribbons alternates from one turn to the next, so thatalso the electromagnetic fields of the currents are short-ranged.

II. BRIEF DESCRIPTION OF THE DRAWINGS

A more complete appreciation of the present invention and many of theattendant advantages thereof will be readily obtained as the samebecomes better understood by reference to the following detaileddescription when considered in connection with the accompanyingdrawings, wherein

FIG. 1 shows part of a cross section of an MP, MP-Plus, MP-A or MP-Tmachine.

FIG. 2A is a schematic cross section of an MP machine in which themagnet tubes are stationary while the rotor is rigidly connected to, androtates with, the axle.

FIG. 2B is a schematic cross-section of an MP machine in which the rotoris stationary while the magnet tubes are rigidly connected to, androtate with, the axle.

FIG. 3A is a perspective view with a partial cut-out of a machine as inFIG. 2A, wherein the rotor is of an insulating material in which anS-ribbon is embedded.

FIG. 3B is a perspective with a partial cut-out of a machine as in FIG.2B, wherein the rotor is of an insulating material in which an S-ribbonis embedded.

FIG. 4A is a schematic plan view of three S-ribbons in the rotor of anMP-T machine.

FIGS. 4B and 4C are flattened-out cross sections of S-ribbons in therotor of an MP-T machine in three layers (B) and compacted into twolayers (A).

FIG. 4D is a semi-schematic illustration of current flow in an MP-Amachine with a rotor constituted of three concentric, mechanically fusedbut electrically insulated rotor layers.

FIG. 5A shows mutually insulated adjoining parts of S-ribbons in therotor rim, i.e. above or below the XX lines in FIG. 4A, including roundholes for the insertion of plugs.

FIG. 5B shows possible S-ribbon arrangements in the cross section of therotor body and relates them to S-ribbon positions in the rotor rim.

FIG. 5C shows the cross section of a screw-in plug for one of the roundholes in FIG. 5A that will establish electrical connection betweenadjoining sides of S-ribbons.

FIGS. 5D and 5E are similar to FIGS. 5A and 5B but show a still moresimplified and presumably more cost-effective construction.

FIG. 5F shows a plan view of part of a rotor with S-ribbon parts in therims constructed as in FIG. 5D but, at lines XX, with three rather thana single mildly twisted wire bundle feeding from the rotor body intoeach side of the S-ribbon parts in the rims.

FIG. 6A as FIG. 5A but enlarged and with an oval instead of a roundhole.

FIG. 6B shows a cross section of a “drop-in plug” for making independentelectrical connections between the outside and adjoining parts of anS-ribbon.

FIG. 6C shows a cross section of a “drop-in plug” for making anelectrical connection between the outside and the left part, but not theright part of an S-ribbon.

FIG. 7 shows a cross section of an MP, MP-Plus, MP-A or MP-T machinewith stationary magnet tubes, flared rotor, inside propeller and nocentral axle, for pumping fluid.

FIG. 8 is the same as FIG. 7 but with a different propeller arrangement.

FIG. 9 as FIG. 7 but with barrel-shaped rotor and with outsidepropeller.

FIG. 10 shows a selection of possible magnet arrangements for MP-A andMP-T machines.

III. DESCRIPTION OF PREFERRED EMBODIMENTS

Referring now to the drawings, wherein like reference numerals designateidentical or corresponding parts throughout the several views, thepresent invention will now be described.

Basic Construction and Cooling of MP-A and MP-T Machines

FIG. 1 shows the basic MP-machine geometry in cross section, includingmachine axle 10, rotor 2 and inner and outer magnet tubes (5 and 6). Themagnet arrangement is optional and is here shown as a Hallbacharrangement of alternating radial and tangential magnets as indicated bythe N and S symbols (for “north” and “south”) that show their respectivedirection of magnetization. As seen, this alternates between N poles ofouter magnets 6 facing S poles on inner magnets 5 and vice versa. Theareas between such magnetic pole pairs are the “zones” of strong radialmagnetic flux density B whose sense of direction changes from one zoneto the next, while the spaces between the zones are the “gaps” whichhave low or no magnetic flux.

Channels 45 and 46 between neighboring radial magnets on either side ofrotor 2 may favorably be employed for channeling cooling fluid in axialdirection. Optionally, such channels may be open to the rotor surface asin FIG. 1 or they may be closed by some barrier, e.g. of fairly thinplastic sheet material.

In preferred embodiments, the channels are left open as in FIG. 1 andthe cooling fluid is a liquid instead of a gas, e.g. is water instead ofair. The use of water increases the efficiency of possible cooling. Thisaspect of MP machines has been discussed in the patent application ref.1 as follows:

For any coolant flowing with velocity v_(C) through cooling channels ofcross sectional area A_(C) so as to transport V_(C)=A_(C)v_(C) ofcoolant volume per second, a temperature increase ΔT of the coolantremoves heat at the rate of

q[watt]=V _(C) cdΔT  (1)

where d is the mechanical density and c is the specific heat of thecoolant. For water as a coolant, it is d=10³ kg/m³ and c=1 cal/(g °C.)=4.2 [joule]/10⁻³ [kg ° C.] for

q _(water)=4.2×10⁶[joule/° C.]V _(C)[m³/sec]ΔT[° C.]  (2)

Hence, for example, water cooling through an A_(C)=1 cm² gap area perzone, at a flow rate of v_(C)=1 m/sec=2.3 mph for V_(C)=0.1liter/sec=10⁻⁴ m³/sec, with a ΔT=10° C. temperature rise between inletand outlet, will extract heat at the rate of q_(water)=4.2×10⁻³ watt≈5.6hp. With the machine loss due to friction and Joule heat, L, beingtypically only about 5% or less of the machine power, this means thatthe indicated 1 m/s water flow through 1 cm² cooling channel pre zone,will at 10° C. temperature rise adequately cool a machine withW_(M)>˜100 hp per zone. This cooling rate will satisfy the needs for allbut very large machines. Say, a W_(M)=100,000 hp machine for a utilitywith N_(Z)=100 zones might require a 1 m/sec water flow through an areaof A_(C)=10 cm² or a moderately faster flow or larger temperature risewith a smaller cooling channel cross section. Cooling with air, forwhich cd of eq. 1 is in the order of 1000 times smaller than for water,but which is amenable to much faster flows at comparable expenditure ofpumping energy, can be similarly effective. These considerations applyindependent of the particular construction of the rotor and thus applyalso to MP-A and MP-T machines, except that their rotors may becomesmodestly hotter on account of their coverage with insulating material aswell as the insulation between S-ribbons that are parallel to the rotorsurfaces and thus transverse to the heat flow. Even so, on account ofthe typically small thickness of rotors, and the fact that bulk of thewaste heat is generated in the rotor, cooling should always be easilyaccomplished.

For the case of water exposure, all surfaces of MP-A and MP-T machineswill preferably be protected by a smooth, corrosion resistant andlow-friction permanent covering, such as of paint, varnish, lacquer orany other protective coating that may be painted on, or sprayed orapplied in any other desired suitable manner. Such a surface coating, onboth rotor surfaces as well as all inner and outer magnet tube surfaceswill at the same time ward off internal short-circuits in the machine,and will assist in smooth relative motion of rotor and magnet tubes.

General Considerations on Rotating Rotors versus Rotating Magnet Tubes

FIGS. 2 and 3 clarify two possible basic geometries of simplecylindrical MP machines, namely (i) with rotating rotor in the gapbetween stationary magnet tubes (FIGS. 2A and 3A), and (ii) ofstationary rotor and rotating outer and inner magnet tubes (FIGS. 2B and3B). In the first case, i.e. in FIG. 2A, rotor 2 is rigidly fastened tomachine axle 10, namely via drivers 61, so that in the motor mode itdrives the axle rotation, and in the generator mode is driven by theaxle. Meanwhile magnet tubes 5 and 6 are centered on the axle vialow-friction bearings 35 but are mechanically anchored to thesurroundings, e.g. the machine base plate 19 via supports 25 in FIG. 2A.In the second case, FIG. 2B, the roles are reversed. Now magnet tubes 5and 6 are rigidly joined to axle 10 via parts 29 and 180 to drive axle10 or be driven by it, in the motor and generator modes, respectively.Now rotor 2 is centered on, but does not rotate with, axle 10, namelyvia parts 181 and low-friction bearings 35. As indicated by thedifferent power sources, i.e. DC in FIGS. 2A and AC in FIG. 2B, currentflows through the rotor, as is the case for all MP-machines, andtherefore, in the case of FIG. 2A, has to be supplied to moving rotor 2by brushes 27(n). However, to a stationary rotor, as in FIG. 2B, currentmay be supplied by means of stationary terminals in the motor mode, orpower may be extracted from it through the same stationary terminals.

It may be noted that a central axle may not be needed and that anchoringto any other part of stationary surroundings of machines may be used tocenter rotating components, albeit probably not as satisfactorily.Anyway, from the mechanical viewpoint, either the rotor or the magnettubes may rotate with or without a machine axle. The following are somepertinent general considerations.

Simple MP machines have rotationally symmetric rotors as well asrotationally symmetric magnet tubes. The asymmetry imposed by stationaryterminals to outside power supplies and/or customers is readilyaccommodated by rotating rotors, the currents in which are fed to and/orextracted from the rotor by means of electrical brushes. Also MP-Plusmachines have rotationally symmetric rotors but they do have asymmetricmagnet tubes. These are pairs of N/S N/S poles side by side, relative towhich the power terminals have to remain stationary. This situation,again, calls for rotating rotors connected to the outside by means ofsliding brushes. However, MP-A and MP-T machines have rotationallysymmetrical magnet tubes but rotors with built-in asymmetry, namelyS-ribbons or S-ribbon sections with ends projecting beyond the zones.This situation permits both, rotating rotors and rotating magnet tubes,as shown in FIGS. 3A and 3B. However, while the interconnections betweenrotating rotors and stationary power supplies and/or customers againrequire sliding electrical brushes, as in FIG. 3A, stationary slip ringsas in FIG. 3B can be supplied by means of stationary terminals, therebyeliminating slip rings and brushes.

In summary, the fundamental difference between MP and MP-Plus machineson the one hand, and MP-A and MP-T machines on the other hand, lies inthe morphology of the rotor (2). The rotors of MP and MP-Plus machinesare rotationally symmetrical, as already indicated, whereas the rotorsof MP-A machines comprise at least one conductive S-ribbon 172 in anelectrically insulating matrix (see FIG. 3), and the rotors of MP-Tmachines contain three similar, regularly spaced S-ribbons in any oneseries of consecutive zones (see FIG. 4) each with two terminals forfeeding current in and out.

Operation of MP-A and MP-T Machines

In the course of relative rotation between magnet tubes and rotors, theaxially aligned parts of S-ribbons periodically pass through zones ofradial flux, on to flux-free gaps, to zones of reversed B-polarity, togaps, and on, always such that the Lorentz force due to different partsof any one S-ribbon, i.e. in neighboring zones, has the same rotationalsense and voltages are additive. As a result, S-ribbons generate, or aresubject to, alternating voltages. A single S-ribbon in a rotor willgenerate simple AC current when used as a generator and may be driven bysimple AC current as a motor.

By using two similar but mutually insulated S-ribbons in the same rotor,with uniformly spaced axial sections, two independent AC voltages areinduced that are 90° out of phase. Generators with two such S-ribbonsmay thus be used as two independent power sources, albeit of samefrequency and power. Similarly, given phase control of the input power,motors with two S-ribbons could be optionally driven by one or two powersources of same controlled frequency and thereby be operated with theequivalent of “field weakening.”

Finally, three independent, similar, uniformly spaced S-ribbons in thesame machine, as depicted in FIG. 4, will produce three-phase current inthe generator mode and may be operated with three-phase current in themotor mode. Such machines are dubbed MP-T machines as already indicatedabove. These can be built with stationary magnet tubes and rotatingS-ribbon rotors, as in FIG. 3A, in which case slip rings and brushes arerequired. Sip rings and sliding electrical brushes become unnecessary,however, when stationary S-ribbon rotors are used in conjunction withrotating magnet tubes, as in FIG. 3B.

A considerable aid in the construction of all MP machines is the factthat the two magnet tubes, i.e. the outer 6 and the inner magnet tube 5,remain closely aligned due to the strong magnetic attraction between thepaired opposing N and S poles. This alignment persists up to the highestpracticable currents strengths, as limited by the maximum machinetorques that rotors can support mechanically.

In FIG. 3A, with rotating rotor, brushes 27(1) and 27(2) are needed tolead currents into and out of the rotor. These brushes are rigidlyconnected to outer magnet tube 6 and slide on slip rings 34(1) and 34(2)situated on a projection of rotor 2 beyond the length of the magnettubes. In the motor mode, rotor 2, and thence axle 10, spins on accountof the Lorentz forces that act on the current through the radialmagnetic flux between the opposing pole pairs in magnet tubes 5 and 6.These remain stationary, being mechanically anchored to the outside, inthis figure via supports 25 on the base plate.

FIG. 3A shows a perspective view of the machine of FIG. 2A but with apartial cut-out of outer magnet tube 6 so as to reveal rotor 2 withembedded S-ribbon. Magnet tubes 5 and 6 remain in radial alignment onaccount of the strong mutual attraction of the paired magnetic poles inthem, as already pointed out. These generate a radial flux density B ofalternating sense of direction in parallel axially extended zones thatin preferred positions coincide with the straight segments of theS-ribbon. Rotor 2 is rigidly connected to axle 10 via structures 61,while inner magnet tube 5 is centered on axle 10 via parts 26 andlow-friction bearings 35 (not shown here but seen in FIG. 2A). Outermagnet tube 6 is centered on axle 10 and remains stationary, in thisfigure on account of parts 25 mounted on base plate 19 that alsosupports bearings 35 of axle 10 via support posts 23 in accord with FIG.2A.

Electrically conductive but mutually electrically insulated slip rings34(1) and 34(2) are formed from metal overlays on an extension ofinsulating rotor 2 with embedded S-ribbon. Slip ring 34(1) is directlyelectrically connected to one end of the S-ribbons as indicated in thedrawing, while an extension of the other end of the S-ribbon iselectrically connected to slip ring 34(2) via S-ribbon end part 175 thatpasses underneath slip ring 34(1) from which it is electricallyinsulated. Brushes 27(1) and 27(2) are rigidly mounted to, butelectrically insulated from, outer rotor 6 or the machine housing or anyother suitable stationary part. They slide on slip rings 34(1) and 34(2)via brush holders that are symbolized by strips 170(1) and 170(2) andcomprise suitable brush loading springs or other devices not shown.Brushes 27(1) and 27(2) are electrically connected to the terminals ofAC power supply 171 via cables 40 to power the machine in the motormode. In the generator mode, power supply 171 is replaced by a powersink or consumer of the generated AC current.

In the case of an MP-T machine with stationary magnet tubes, rotor 2will generate or use 3-phase current if it comprises not just oneS-ribbon as in FIG. 3A, but three equally spaced, mutually insulatedS-ribbons, such that electrically the phases of the generated orsupplied current are spaced 120° apart. Mechanically/electricallychanging an AC machine as of FIG. 3A to a three-phase machine, requiresthe provision of four additional slip rings, say, 34(3) to 34(6), plusfour brushes, say, 27(3) to 27(6) that are connected to the terminals ofthe three poles of a three-phase power supply or three-phase consumer,in addition to brushes 27(1) and 26(2), shown in FIG. 3A. Also, themutual insulation among all six slip rings and six brushes need to bemaintained. Two simultaneous AC phases, whether electrically 180° or120° apart, may be accomplished in the same manner but with only fourmutually insulated brushes that slide on four mutually insulated sliprings

Morphology and Operation of Individual “S-Ribbons”

As discussed, all MP-A and MP-T machines contain rotors with conductiveS-ribbons 172, that are shaped such that, periodically, they coincidewith the zones within the magnet length of the inner and outer magnettubes, whether through the rotation of the rotor or the rotation of themagnet tubes.

The width of an S-ribbon and of the gaps between adjacent turns of anS-ribbon, is preferably, but not necessarily, made equal to the magnetwidth as projected on the rotor mid-line, L_(m), which is equal to thewidth of the gaps in the magnet tubes, as indicated in FIG. 4.Correspondingly, on rotation the induced voltage for a single S-ribbonchanges sinusoidally as follows:

The width of the S-ribbon embedded in the rotor should preferablyapproximate the width of the zones, and thus in total cover about onehalf of the rotor circumference. Also, in order to prevent eddy currentsin the ribbon when the rotor rotates, the ribbon should preferably besubdivided into mutually electrically insulated parallel strands thateach are no wider than 1/16.″ In operation, beginning, say, with theaxially oriented ribbon sections centered on the zones (of axial lengthL), a circumferential velocity v_(r) will induce the voltage V₁=v_(r)LBin each of the ribbon sections but (essentially) none between zones.Thus if there are N_(z) uniformly spaced zones and N_(z) correlatedribbon sections, the maximum induced machine voltage will be

V_(Mmax)=N_(Z)V₁=N_(Z)v_(r)LB.  (3)

Further, if the zone width, i.e. the circumferential width of themagnets as projected on the rotor mid-line, is L_(m), if the gapsbetween the zones are of the same width, and the rotor diameter is D, itwill be

N _(z) =πD/2L _(m)  (4)

i.e. with

ν=v _(r) /πD  (5)

for

V _(Mmax) =πDv _(r) LB/2L _(m)=π² D ² νLB/2L _(m.)  (6)

The axially oriented sections of the ribbon will in one rotor revolutiontraverse N_(z)/2 zones of same radial orientation of B, i.e. at rotorrotational velocity, ν, at time intervals

T=2/N _(z)ν=2πD/N _(z) v _(r.)  (7)

Thus starting at t=0 with the S-ribbon sections centered on zones, thevoltage between the ends of the S-ribbon will alternate as

V _(M) =V _(Mmax) cos(πN _(z) νt)=(π² D ² νLB/2L _(m))cos(πN _(z)νt)=(πDv _(r) LB/2L _(m))cos(N _(z) v _(r) /Dt).  (8)

When the machine is operated as a generator at rotational speed ν,external terminals contacting the two slip rings will therefore pick upan alternating (i.e. AC) voltage as in eq. 8, except for a factor (1−

) wherein

is the machine loss composed of approximately 2% friction and windage,plus the Joule heat loss and (the generally negligible) electrical brushloss. Alternatively, an applied AC voltage, boosted by the factor 1/(1−

) will drive the same machine as a motor with rotational speed ν.

The delivered electrical power, W_(M), and conversely the deliveredmechanical power in the motor mode, will be determined by the currentflowing through the ribbon, i_(M), as

W _(M) =V _(Mmax) i _(Mmax)/2  (9)

The current is principally limited by the ohmic loss in the ribbon viathe machine efficiency in much the same way as it is in Multipolar andMultipolar Plus machines. The already obtained estimates as to powerdensity of those machines, and in particular Multipolar Plus machines,are therefore applicable. Also the data on voltages and currents as afunction of machine parameters are much the same as for MP Plusmachines. In fact, since with stationary rotors there are no brushes atall, MP-A and MP-T machines are liable to be the most favorable of allMP machines.

Construction of MP-T Machines

Advantageously, the S-ribbons will be composed of mutually insulatedwires of no more than 1/16″ diameter, so as to inhibit eddy currents. Ina preferred configuration, those wires may be mildly twisted andcompacted to approximate close-packing so as to achieve maximum possiblecurrent densities for optimal power density of the machines.

Changing the S-ribbon width within an otherwise unchanged machine, willchange the wave form of an alternating current Specifically, assuminguniform current density over the width of the ribbon, widening theS-ribbon beginning with a single strand that is much narrower than thezone width, will change the induced voltage from an abrupt on-off waveform with alternating “on” directions, over gradually less sharplydefined transitions between “on” and “off,” to sinusoidal when zone andribbon width are equal. Further widening of the S-ribbon will causedecreasing voltage or torque amplitudes for motors and generators,respectively, and rising waste heat. This is so because leading andtrailing edges of the individual ribbon segments will be increasinglyexposed to opposite directions of B and thus opposite induced voltagesor torques. Meanwhile, the total induced voltage or torque, being due toall strands in the ribbon, will rise with the width of the ribbon up tothe point that it has the width of the zones. Thereafter the inducedvoltage and torque decrease, until almost all of the input energy isconverted into waste heat, namely when the S-ribbon width becomes equalto the spacing between zones of same B orientation. From this analysisit follows that the optimal ribbon width will be near the zone width.Even so, as will be shown below, reducing S-ribbon widths in the rotorbody to ⅔ of the zone width, permits making S-ribbons simply rectangled.A further simplification of rotor construction, especially in cases inwhich the rotor wall thickness is significantly smaller than the zonewidth, is possible by assembling S-ribbons from roughly equiaxedrectangled units.

The above proviso “assuming uniform current density over the width ofthe ribbon” touches on an important issue, since current uniformity isby no means assured, as follows: In a homogeneous conductive ribbon, thecurrent density, and thereby the incremental contributions to theLorentz force and machine torque, will be roughly uniform while theribbon is centered on a zone. However, in general, only that ribbon partwhich is momentarily in a zone is subject to electromagnetic inductionand the associated opposing induced voltage that is absent in the gap.Thus, for the moment contemplating the ideal case of B=0 in gaps betweenzones, the ribbon that is partly in a zone and partly in a gapessentially acts like two parallel conductors to which differentvoltages are applied, one in the gap and the other in the zone with netlowered voltage. At fixed total current through the ribbon, therefore,the current density will be considerably lowered in the zones, where theLorentz force and induced voltage are generated, to disastrously reducethe machine torque at given machine current and speed, and similarly thecurrent in the case of a generator. In fact, the magnitude of B variesalmost sinusoidally along zones and gaps. The associated gradients ofmagnetic flux density, B, cause just the same effect, namely of currentcrowding in preference of areas of lower B.

For the case of S-ribbons with relatively fixed positions of theconductors in them, a solution to this problem is to alternate thepositions of leading and trailing edges of the ribbon from one zone tothe next so that the relative portions of ribbon width in zones and gapsare alternating and the above effect is eliminated over any even numberof successive axial segments of S-ribbon. Fortuitously, such alternationbetween leading and trailing edges of the ribbon from one zone to thenext will result automatically if at the turns between successive ribbonsegments, the ribbon is rotated about an axis parallel to the rotorradius but not about its own axis, e.g. as suggested in FIGS. 3 and 4.

According to the present invention, another advantageous solution is tomake S-ribbons in the form of slightly twisted wire bundles, e.g. of twoto five full turns along the length of the rotor body in the gap betweenthe magnet tubes. In such a bundle, each wire will sample all values ofthe magnetic flux between its two ends. Thereby the current density inthe bundle will become nearly uniform, independent of the S-ribbonposition relative to the nearest zone center. Herein, for protectionagainst eddy currents, the wire diameter should not exceed 1/16″.

Machine Controls

As seen from eq. 8, the voltage of MP-A and MP-T machines isproportional to the rotation speed,—just as it is for MP and MP-Plusmachines, but the frequency of the current or voltage, as the case maybe, is also proportional to the rotation speed. Correspondingly, speedcontrol of MP-A and MP-T machines is liable to be done through frequencycontrol, via inverters, while as in all members of the family of MPmachines, the current controls the torque. Machine control via invertersappears nowadays to be very prevalent for AC as well as 3-phase motorsfrom low frequencies to hundreds of Hz. In case of an MP-A or MP-Tmachine with N_(z) zones, in particular, an inverter with up toν_(V)=400 Hz=24,000 rpm voltage/current frequency control could controlup to a machine rotation frequency of

ν=ν_(V) /N _(z)=400/N _(z)  (10)

according to eqs. 6 and 7. With a maximum of about N_(z)=200 for thelargest machines, this example yields control up to ν=120 rpm, whichwill be adequate for the largest machines.

Relative Merits of Brushed and Brushless Machines

The basic properties of MP-A machines outlined in the previous section,are independent of the choice between moving rotor or magnet tubes inaccordance with FIGS. 2 and 3 below. In line with the precedingdiscussion, the consequences of this choice are important because of therelative advantage of brushless operation when the magnet tubes spin andthe rotor is at rest, as illustrated in FIGS. 2B and 3B. Very importantherein, and as already stressed, is the fact that with spinning rotor,each S-ribbon requires two brushes (or brush “sites”) and two mutuallyinsulated slip rings, i.e. altogether four brush sites and four sliprings for two S-ribbons, and six brush sites and six slip rings forthree-phase machines with stationary magnets. Fortunately in thisconnection, unlike the cases of simple MP and of MP-Plus machines, inwhich the width of brushes is limited by the magnet width, in thepresent case the brush sites may be spread out over at least asubstantial part of the rotating slip rings so that the slip rings donot need to be excessively wide in axial direction. Even so, on accountof needed moisture access and cooling (see “Metal Fiber Brushes,” D.Kuhlmann-Wilsdorf, Chapter 20 in “Electrical Contacts: Principles andApplications,” Ed. p. G. Slade, Marcel Dekker, NY, 1999, pp. 943-1017)the brush length in sliding direction cannot be made arbitrarily long,and therefore in large machines, subdivision of brushes within any onebrush site will typically be needed, which in turn requires thecorresponding brush holders. In sum, therefore, the complication throughsix sets of electrical brushes and six slip rings for 3-phase power,MP-T, machines with stationary magnet tubes, can be substantial to thepoint of perhaps making large three-phase machines with stationaryrotors impractical.

The complication of rotating magnet tubes with their larger weight, ascompared to lighter rotating rotors, in regard to machine constructionaccording to FIGS. 2B and 3B, appears to be rather more benign, or theremay be none. In addition, machine weight and volume are beneficiallyimpacted by the omission of slip rings and brushes. Therefore at thispoint the relative advantages and disadvantages of the two choicesappear to be as follows:

Favorable Consequences of Spinning Magnet Tubes Versus Spinning RotorsElimination of brushes and slip rings will:

-   -   Modestly reduce machine length, volume and weight;    -   mildly decrease capital cost of machine;    -   reduce machine ownership cost by up to an estimated factor of        two;    -   simplify machine cooling;    -   increase resistance against environmental damage;    -   with all components covered with protective coatings, increase        ability to operate while immersed in water, up to perhaps        sustained operation in sea water;    -   greatly increased possibility of multiple machine uses through        generating sub-units and connecting these to external        components;

Unfavorable Consequences of Spinning Magnet Tubes Versus Spinning Rotors

Spinning of magnet tubes will:

-   -   at least double inertial forces and expected vibration and        mechanical noise;    -   decrease lifetime of bearings which will partly offset the        ownership cost reduction following from the elimination of        electrical brushes and slip rings;

Neutral Consequences of Spinning Magnet Tubes Versus Spinning Rotors

Changing from spinning rotor to spinning magnet tubes is likely to havenegligible effect on:

-   -   machine controls;    -   basic machine operation;    -   basic relationships among machine parameters;    -   machine efficiency.

The advantages for brushless MP-A machines increase with the number ofS-ribbons involved, i.e. are especially strong for brushless MP-Tmachines, while the disadvantages are little dependent on the number ofS-ribbons. Special emphasis herein may be given to the possibility ofoperating brushless MP-A and MP-T machines while fully immersed inwater, even sea water that results from the fact that all parts ofbrushless MP-A and MP-T machines may, and in favored embodiments willbe, completely protected with electrically insulating and chemicallyinert coatings, as was already stated in section “Basic Construction andCooling of MP-A and MP-T Machines” above. For podded ship drives use ofMP-A and MP-T machines will be a great advantage indeed. Anotherquestion, further discussed below, is the power density of MP-T machinesrelative to simple MP and MP-Plus machines.

Geometry, Manufacture and Power Density of MP-A and MP-T Machines

Fraction of Rotor Cross Section that Carries Current with S-Ribbons

In line with the above explanations and listing, MP-A and MP-T machinesconstructed in accordance with FIGS. 2B and 3B as compared to 2A and 3Aor similar, are expected to have great advantages. In particular, theelimination of brushes and slip rings will shorten the machine andreduce its volume, and probably decrease construction cost and ownershipcosts, as further discussed below.

The construction of MP-A and MP-T machines is constrained by theexpected need to assemble the machine from its parts and be amenable todisassembling and re-assembling for maintenance or repairs. Therefore,the rotor parts, dubbed “rotor rims,” protruding beyond the magnet tubes(i.e. in FIG. 4A beyond the XX lines) should preferably have the samecross sectional dimensions as those inside (dubbed “rotor body”), and inany event should preferably not have a wider wall width and/or largerdiameter than the rotor body, since this would interfere with slidingthe rotor into and out of the machine. In accordance with FIG. 3, thisrestriction presents no difficulty for AC machines with just oneS-ribbon in any one periodicity distance between zones, but isproblematical for machines with multiple S-ribbons because ofunavoidable crossovers of S-ribbons outside the magnet tubes toaccomplish the connections between neighboring turns of the S-ribbons.

The case of three S-ribbons in any one periodicity distance, i.e. inparticular MP-T machines with a single rotor, is of the greatestpractical importance herein, and it suffices to consider it becauselarger numbers of S-ribbons per periodicity distance may be treated bymeans of rotors constituted of two or more mechanically fused butelectrically insulated rotor layers as clarified in FIG. 4 wherein therotor comprises three layers and no division into sub-units is assumed.In that case at the moment that the alternating current makes the rightterminal of current source 171 positive, the current enters the rightterminal of layer 1, shown above line XX, and passes along the length ofthe rotor body, first at the momentary position of zone 1, turns through360 below line XX at the bottom of the drawing, returns along zone 2 andso on, as indicated by the arrows, until it has passed zone N to reachthe left terminal of rotor layer 1. From there the indicated cableconnection leads the current to the right terminal of layer 2, in whichlayer the current again travels through all of the zones until itreaches the left terminal of layer 2. The indicated cable then leads thecurrent to the right hand terminal of layer 3, for another circuitthrough zones 1 to N in layer 3 until the current emerges at the leftterminal of layer 3 and from there through a cable connection to thepower supply 171.

As will be noted, throughout the current will experience the same senseof Lorentz force, as in FIG. 4D it travels down when the shading slantsfrom bottom left to top right, and travels up when the slant is from fopleft to bottom right. In this manner, then, the current executes 3N“turns” in its travel between the two poles of power supply 171.

Since the current alternates, the current direction oscillates, andmeanwhile the zones, being due to magnet poles affixed to rotatingmagnet tubes 5 and 6 will move horizontally in the orientation of FIG.4D. The machine motor control will have to be arranged that issynchronizes these two effects, i.e. the alternating sense ofmagnetization due to the moving zones, and the alternating currentdirection on account of the alternating voltage direction supplied bythe power source. For the sake of clarity, FIG. 4D shows only oneS-ribbon per layer, i.e. the case of an MP-A machine, operated by simpleAC power. The case of 3-phase is directly derivable from FIG. 4D byusing three S-ribbons as in FIGS. 4A and 5.

Except for FIG. 4D, already discussed, the case of three S-ribbons perrotor in an MP-T machine is considered in FIGS. 4A to C and 5. Thesedemonstrate by means of FIG. 4B that the most simple case will require arotor wall width of at least three S-Ribbon thicknesses in the rotorbody, but that by mechanical compaction as in FIG. 4C this can bereduced to two S-ribbon thicknesses.

Rearrangement, e.g. as in FIG. 5B, including paralleogrammatic slabs andinto simple rectangled bars as in FIG. 5E, can increase the volumeoccupancy of conductors in the rotor cross section above ⅚^(th)=83% inFIG. 4B, namely to near full occupancy, assuming near close packing ofthe individual S-ribbon through compacting. In any event, there willhave to be a minor percentage of insulating material within S-ribbonsfor the suppression of eddy currents, as well as between S-ribbons a, b,and c (labeling these according to their relative positions), and on theouter and inner rotor surfaces. Together these non-conducting componentswill reduce actual volume occupancy of conductors in the rotor body toabout 94% at the most.

Also the rotor rims protruding beyond the magnet tubes can be reduced totwo S-ribbon thicknesses, indeed more easily than the rotor body. Thisis demonstrated in FIG. 4A, wherein local three-layer thickness areasthat would result from 180° turns in the form of circular annular rings,are avoided through narrowing the S-ribbons near their apex.Accordingly, at constant external rotor rim wall thickness, thethickness of the conductors in rotor rims may be approximately doubledwhere there is only one layer, e.g. in particular the outermost piecesthat comprise holes 177. Doing this will at the same time mildlyincrease weight, decrease electrical resistance, and improve thestability and serviceability of insulating screw-in plugs 178 andterminals 176.

Possible Practical Design and Manufacture of MP-T Machines

FIG. 5 presents a modification of FIG. 4. Herein, the compaction ofthree similar S-ribbon sets, again labeled a, b and c according to theirrelative position, into a two-layer thickness (plus insulating jointsbetween the ribbons and insulating surface layers 184 on the rotor) ismade simpler and more efficient in FIGS. 5B and 5E compared to FIGS. 4Band 4C. Also, the “rotor rims” beyond lines XX in FIGS. 4 and 5 areredesigned. Namely, as shown in FIG. 5A, the upper rotor rim, shown inrelation to the rotor body in FIG. 5B, involves zero, one and two layersof S-ribbons, whereof one-layer thicknesses are in preponderance. Asalready stated, in preferred embodiments the metal thickness in thoseone-layer areas will be doubled, such as to make the rotor rim wallthickness equal to the compacted wall thickness of the rotor body. Alsothe cross sectional arrangement of the layers at the joint line needs tobe adjusted to permit butt-joining of rotor rim and rotor body alongline XX. Specifically, in FIG. 5, in which the circumferential width ofthe S-ribbons as equal to the zone width is retained in the rotor body,this is done through thickness beveling as indicated by the dotted linesat lower left of FIG. 5A. Herein S-Ribbon cross sections in the rotorbody are parallelogrammatic as at left in FIG. 5B.

By decreasing the S-ribbon width in the rotor body to ⅔ of the zonewidth, and correspondingly adjusting the shapes of the S-ribbons in therotor rim according to FIGS. 5D and 5F, S-ribbons in the rotor may bemade rectangled as in FIGS. 5E and 5F. This will simplify rotorconstruction.

In either case, according to the present invention, S-ribbon parts inthe rotor body may advantageously be made in the form of mildly twistedcompacted bundles of mutually insulated wires of no more than 1/16″diameter so as to inhibit eddy currents. A particular advantage ofmildly twisted wire bundles has already been outlined above. It is thatthe wires in them will sample the magnetic flux density within the wholeS-ribbon width and thereby eliminate periodic shifting of currents fromregions of higher magnet flux density, i.e. at the zone centers, toregions of lower flux towards the zone edges or even beyond. Therebywire bundles are expected to decrease electronic noise. Further, thediscussed current shifting in S-ribbons will mildly lower the value of Bin the current path and thus impair machine power density. Additionally,according to the present invention, mildly twisted and compacted wirebundles are expected to significantly lower rotor construction costsbecause they reduce the number of, and are much stiffer than, the itemsto be assembled into a rotor, namely ≦ 1/16″ wires or bars.

For further clarification of the geometry involved, the momentarylocation of the zones, namely at the moment of symmetric positioningrelative to the a-ribbons, are shown by means of horizontal shading inFIG. 5E and by diagonal shading in FIG. 5F.

FIGS. 5A and 5B as well as FIG. 6 indicate means for dividing machinesinto sub-units that may be employed in independent machine functions,namely via holes 177 and exchangeable plugs 178, 195 and 196 in FIG. 5Dthat are further discussed below. No division of the rotor intosub-units is envisioned in FIGS. 5D and F. Therefore no holes and plugsare shown in FIGS. 5D and 5F, but these features could be readily added.Also insulating barriers 190 as in FIG. 5A are required to prevent shortcircuiting between connections to different outside connections, i.e. atthe “in” and “out” terminals of sub-units. In machines withoutsub-units, barriers 190 are only required at the “in” and “out” machineterminals, as shown in FIG. 5D electrical connections to an external3-phase power source (not shown). FIG. 5D shows the “in” and “out”terminals separated by an extra three S-ribbons in the rim so as togreatly reduce the danger of short-circuiting. This would be an extraprecaution that is strictly optional.

Thicker solid rim edges will be useful in fitting the rotor rim withelectrical connections. Thereby, optionally, a multiplicity and up toall S-ribbon “turns” are prepared for electrically connecting to outsidecomponents such as power supplies and power consumers, i.e. for dividingthe machine into sub-units for multiple machine uses.

Most simply, the ribbons inside of the rotor body as well as in therotor rims could be made in one continuous length, of parallel, axiallyextended elements (e.g. “wires” or “rods”) whose width incircumferential direction would be, say, 1/16″ or less in order tosuppress eddy currents, as already indicated above. However, inaccordance with the present invention, and as implied in FIGS. 4, 5 and6, favorably rotors will be made in three sections, namely a rotor body(inside the XX lines in FIGS. 4 and 5), and two rotor rims, one each oneither side of the XX lines indicated in FIGS. 4A and 5A. These would beconductively butt-joined by means of soldering, conductive glue or anyother suitable method. Further, in preferred embodiments, comprisingsub-units that may be used largely independently of each other, e.g. asmotor(s), generator(s) and/or parts of transformers, S-ribbon pieces inthe rotor rims may (i) be made of solid metal and (ii) provided withinsulating barriers 190 to electrically separating sub-units, and (iii)holes 177 or slots (not necessarily round as in FIG. 5A or oval as inFIG. 5B) that may be fitted with releasable “screw-in” plugs (178 inFIG. 5) or “drop-in plugs (195 and 196 in FIG. 6) to make electricalconnections between successive “turns” and/or to outside components suchas power sources or receivers, as may be desired.

In butt-joining rotor bodies and rotor rims, care should be taken tominimize unintended electrical connections between different elementssince such degrade machine efficiency. Preferably, every a S-ribbon partin a rotor rim should be joined to its corresponding a S-ribbon part inthe rotor body, across the conductive joints, without generatinginadvertent electrical connections between a S-ribbon and b or cS-ribbon parts. Similarly every b and c S-ribbon part should preferablybe conductively joined across the conductive joints to its correspondingb and c S-ribbon part, without generating inadvertent electricalconnections to other parts. As an aid to this end, according to thepresent invention, prior to soldering or conductively gluing together arotor body and rotor rim, matching shallow grooves, e.g. of one to a fewmillimeter depth and of less than ⅛″≈3 mm width, may be engraved on bothsides, and said shallow grooves may be filled in with insulatingmaterial.

In preferred embodiments, and as indicated in FIG. 5F, a plurality ofneighboring, mechanically joined but electrically insulated twisted andcompacted wire bundles in a rotor body may be electrically conductivelyjoined to a solid corresponding part in a rotor rim. In FIG. 5F, threewire bundles each are so assembled as indicated by broken lines Theadvantage of doing so is as follows: Advantageously, twisted compactedwire bundles will be roughly equiaxed, and also advantageously, onedimensions of such wire bundles will correspond to the width of therotor body wall thickness, as indicated in FIGS. 4 and 5. This parameteris favorably determined from considerations of overall machineconstruction, and different considerations will be used to determine therotor diameter, number of zones, zone width and the width of theS-ribbon parts in the rotor rim. Discrepancies in the so determinedoptimum desired values of the different parts may be more readilyreconciled by the indicated assembly of a multiplicity of twisted wirebundles into one S-ribbon width in a rotor body.

Note also in FIGS. 4A and 5A that, in preferred embodiments, the widthof the rims is only about 2L_(m), i.e. about twice the zone width and,typically, in the order of twice the rotor wall width, for a totalmachine length of

L _(m) =L+4L _(m)  (12)

with L the length of the magnet tubes. Under almost all circumstancesthis will be significantly shorter than achievable with any brushed MPmachines with their associated slip rings, including also MP-Plusmachines.

The indicated simplified construction of rotor rims incorporating solidmetal, instead of laminated or otherwise subdivided, S-ribbon sections,e.g. shaped as in FIG. 4A or 5A or similar, is possible because there isno need for eddy current barriers outside of the magnetic flux of zones.However, in simply butt-joining the a-, and similarly b- and c-parts ofS-ribbons of rotor body and rotor rims, the previously discussed featureof reversal of leading and trailing edges of S-ribbons in successivezones, in order to prevent crowding of current into areas of lowmagnetic flux, is lost. Thereby a significant fraction of the machinetorque could be lost, as the solid parts in the rotor rims would permitcurrent transfer between ribbon parts within and outside of zones.

According to the present invention this problem is avoided by making a,b and c S-ribbon sections in the rotor body from bundles of mutuallyelectrically insulated <˜ 1/16″ diameter wires that are lightly twistedand compacted, extruded or rolled into the shapes of a, b and cS-ribbons (the same if the configuration of FIG. 5B is chosen).Compaction or rolling as for FIGS. 4B and 5B will be facilitated if thewires are smooth, round and glued together with a thin layer ofinsulating adhesive that softens above machine use temperature, e.g.above 100° C., and the bundles are shaped while heated to a temperatureat which the adhesive is suitably softened. For the purpose of avoidingthe discussed shifting of current from zones into gaps between zones,the bundles should have at least one full twist in length L of themagnet tubes, or arbitrarily more twist, since this will equalize theimpedance (effective resistance) over the S-ribbon cross section.

Since by their nature, the cross sections of twisted bundles of fiberstend to be equiaxed, compacting these into the elongated cross sectionsof the a and c S-ribbons in FIG. 4C, and the stepped cross sections inFIGS. 4C and 5B, may pose a problem. If so, and in any event if for somereason this should be advantageous, the S-ribbons may be constructedfrom more nearly equiaxed rectangular cross sections that are fittedtogether with conductive adhesive, as for example indicated by dottedlines at the right side of FIG. 5B. Most simple may be theparallelogrammatic shapes at FIG. 5B left.

The machine use temperature may be limited by the softening temperatureof the adhesive in the S-ribbons. However, the use temperature ofMP-machines of all types is any-way restricted to the temperature beyondwhich the magnetization of the permanent magnets degrades. Hence,according to the present invention, the softening temperature of theadhesive in the S-ribbons, as well as of the adhesive bonding withinS-units and into a rotor body, and also of the matrix and/or surfacecover material of rotor bodies and rotor rims, do not need to be muchhigher than the expected use temperatures of the MP-A and MP-T machinesat issue, and below the temperature at which the permanent magnetsdegrade.

Different Machine Functions Via Sub-Units, Alternatively and/orSimultaneously

Up to now, S-ribbons were considered to pass once through all zonesabout the rotor, and start and end in close proximity, e.g. inneighboring zones, as in FIGS. 3A and 3B. This is an unnecessaryrestriction. Rather, in general, a single S-ribbon may encircle a rotorn times with n any number smaller or larger than unity, and conversely amultiplicity of S-ribbons may be contained in a single rotor, i.e.essentially a single circuit of an S-ribbon about a rotor may be brokenup into any desired number of sections. Also, multiple mutually isolatedS-ribbons may be placed on top of each other in a rotor. Similarly thestart and end of two S-ribbons may be placed into neighboring zones, orinto any desired positions.

Importantly, any continuous part of S-ribbon, through which a currentmay pass independent of other continuous parts of S-ribbon, constitutesa “sub-unit” that may be used like an individual motor, generator ortransformer winding whose current may be individually controlled andwhose voltage is proportional to the number of passages along separatezones comprised in that sub-unit. This concept for which patentprotection has previously been claimed for MP machines (ref. 1) and forMP-Plus machines (ref. 2) applies also to MP-A and MP-T machines inaccordance with the present invention.

Insulating barriers 190 in FIGS. 5 and 6 are the means by which theend-points of sub-units are established optionally, at one extreme, atevery S-ribbon on both rotor rims, as shown for one rim in FIGS. 5 and6, and on the other extreme at only one rotor rim and only one locationabout the rotor circumference. The latter is the case in FIGS. 3A and3B, wherein the interruption in the S-ribbon is morphologically, but notfunctionally, different from a barrier in the shape of 190 in FIGS. 5and 6. According to the present invention, one may therefore choose toseparate any one S-ribbon into as many sub-units as the number of zonestraversed by in when Lorentz forces are generated, namely by providingbarriers 190 at each end of each zone. However, since in brushedmachines as in FIG. 3A, use of any one sub-unit constituted by anS-ribbon section requires two brushes and two slip rings, more than,say, two sub-units will be practicable only in brushless machines, i.e.as in FIG. 3B, with every sub-unit connected between two terminals (176)and no terminal connected to more than two sub-units.

FIGS. 5 and 6 illustrate a simple method for providing terminalsequivalent to 176 in FIG. 3B. Herein, for clarity, metal parts are givenwith shadings of smooth parallel lines and insulators are cross-hatched.

As a first step, FIG. 5C shows a “screw-in” plug that will establish apermanent low-resistance electrical connection between S-ribbon parts172(1) and 172(r) that had been isolated by barrier 190. Plugs withconductive bodies such as 178 make electrical contact with therespective S-ribbon parts about their whole circumference and thusestablish electrical connection between S-ribbon parts 192(1) and192(r), thereby disabling, temporarily or permanently, any separation ofan S-ribbon into adjoining sub-units. Further, modifications of plugsmay be used to establish connections of S-ribbon ports to outsideelectrical components.

The advantages of screw-in types of plugs like 178 include greatgeometrical simplicity, low boundary resistance between the two S-ribbonparts, and firm permanent installation by means of nut 179 on insulatedthreaded end 193, optionally supplemented by a lock-nut washer or othermeans to prevent not 179 from loosening during use. However, they do notestablish a correlation of contacts between plug and left versus rightside, top and bottom. Also, if cables to the outside should be attachedto screw-in plugs they will tend to become twisted during installationand removal.

Therefore, as a second step, the shape of hole 177 is changed to taperedoval in FIG. 5 AND “screw-in plug” 178 is replaced by “drop-in” plugs195 and 196 or variations thereof. Retaining insulated threaded end 193and nut in conjunction with the tapering assures low contact resistancealso without a screw thread as in plug 178. Specifically, plugs 195 and196 in FIGS. 6B and C illustrate convenient ways of making connectionsto other sub-units in the same machine and/or to outside components suchas power sources, motors and generators. In the case of plug 196 (FIG.6C), electrical connection is made via insulated cable 40(1) from/toonly one of the S-ribbon sides, in this case 192(1), while plug 195 ofFIG. 6B makes independent connection via cables 40(1) and 40(r) from/toboth sides, i.e. 192(1) and 192(r).

In FIG. 6A, the shape of hole 177, i.e. oval in this case, is arbitrary.Any other shape such as polygonal or slot-like, or a combination ofstraight and rounded parts of the periphery may be chosen. The salientfeature is departure from rotational symmetry compared to hole 177 andplug 178 in FIG. 5. In practice, choices as to the morphology of hole177 will be made based on additional considerations such as cost; easeof installation, replacement and interchanges, perhaps while the machineis in operation; minimization of possible errors in installation,replacement and interchanges; and magnitude of internal resistance.

The drop-in nature of plugs 195 and 196 of FIG. 6 avoids tangling and ingeneral sterical interference with and among cables. Cables are depictedas insulated. Such insulation is virtually automatic in line withelectrical engineering practice, but in this case has the particularfeature of being fused with the material of insulating cap 191 that issealed against the outside insulating coatings 184 of ribbon parts 172and barrier 190. This fusing or tight joining is essential for effectivesealing against ambient fluids and therefore long-term serviceability ofmachines, especially in hostile environments, e.g. when fully immersedin sea water or perhaps operating as a pump (e.g. FIGS. 7 and 8),perhaps in chemical plants. For the same reason, i.e. effective sealingagainst ambient fluids, the contact surfaces of cap 191 and washer will179 advantageously be lined with a suitable elastomer, e.g. Viton®.

The use of sub-units has previously been discussed in fair detail,namely in refs. 1 and 2. For the present application a brief outline maytherefore be sufficient: Every sub-unit will deliver as a generator, orwill use as a motor, a voltage in accordance with the number of zonestraversed by its current. Namely, the induced voltage between the endsof an S-ribbon section in a rotor with magnet length L that extends overN_(ZS) zones of magnetic flux density of B and spins with surfacevelocity v_(r) will be

V_(S)=N_(ZS)v_(r)BL=N_(ZS)νπDBL.  (11)

Any particular S-ribbon under consideration, will be essentiallyindependent of any other sub-units, except that, normally, the values ofB, L, D and certainly ν will be the same in all sub-units of a machine.Therefore the voltage applied to, or delivered by, different sub-unitsof a machine will be proportional to N_(ZS), i.e. the number of zonesover which any particular sub-unit extends. Thus it will be possible todrive a certain motor from two or more different voltage sources withdifferent voltages at a fixed speed. This could be useful in order to,say, bolster the machine power at constant speed, i.e. in a variant of“field weakening.”

In the multiple use of sub-units, care may have to be taken not tounbalance rotors through non-uniform currents in different sub-unitsthat will cause the corresponding different forces and stresses aboutthe circumference of a rotor. For this purpose, encirclements by wholenumbers of S-ribbon may be best, especially at low rotation speeds. Orone may for example use three consecutive S-ribbons each one third rotorcircumference long. Or use five consecutive S-ribbons that total tworotor circumferences in length, all with the same current. Or use, say,three pairs of two similar S-ribbons each, distributed over onecircumference. For example the two S-ribbons of one pair could span 45°each, another pair could span 60° each, and a third pair could span 30°each for a total of 2×(45°+60°+30°)=270°, leaving 90° of rotorcircumference free of S-ribbons. Herein, the S-ribbons as well as thefree spaces between them will preferably be pair-wise distributeddiametrically across each other so as to nearly equalize forces andstresses about the rotor and magnet tubes.

Again, with the envisaged mutual electrical insulation among the ribbonsand their respective pairs of terminals (176 n according to FIG. 3B)each of these S-ribbons would function like an independent motor orgenerator. Therefore they may be connected to independent sources orsupply independent power consumers, PROVIDED that all S-ribbons thatoperate in the motor mode are supplied with the same frequency AND areat same phase in the case of AC or have the appropriate phase in thecase of three-phase current. Thus one large machine may simultaneouslydrive a ship propeller, as generator could provide different voltages todifferent circuits, and supply electricity to heaters. This same conceptof simultaneous multiple uses has previously been proposed for simplehomopolar MP machines as also for MP-Plus machines with so-called“radial zig-zags,” see ref. 2. Albeit in both cases a large number ofbrushes and brush holders would be required.

As an example for the application of independent sub-units, that wasalready given in ref. 2, consider a large 1440 Volt MP-A ship drivemachine comprising, say, 144 zones, in which 1200 volts, i.e. 120 zones,are dedicated to turn a variable pitch propeller at a constant 100 rpmspeed but with widely variable torque supplied through a controlledcurrent. Of the remaining 24 zones, 22 could be devoted to supplying 220V alternating current for hotel uses of the ship and the last two zonesfor supplying 20 Volt AC emergency circuits,—which could well berectified into DC. This would make it possible, also, to idle thepropeller while in harbor but still supply the other needs, or in caseof urgent need, e.g. as for a war ship avoiding a submarine threat, todivert all of the power to the propeller and perhaps to drive it fasterby connecting the 120 zones and the 20 zones in series. Or conversely toincrease the “hotel” power at the expense of propeller power, or toextract extra power for cannons or catapults. In fact uses ofindependent sub-units are almost without limit.

More mundanely, for only a single mode of use, or perhaps a few such asfor “field weakening,” the opportunity to let S-ribbons extend over anydesired number of “turns,” i.e. pass through an arbitrary number ofzones, permits great flexibility in the design of MP-A and MP-T machinesto user specifications as to desired rotation speed, voltage andcurrent. This may be done through selectively connecting the input oroutput of different S-ribbons in series or in parallel, as may bedesired,—optionally switching while the machine is in motion since theterminals 176 are permanently at rest.

Expected Machine Efficiency and Power Density of MP-A and MP-T Machines.

The very favorable machine efficiencies and power densities of MP andMP-Plus machines carry over to MP-A and MP-T machines without anyadjustments except for the changes caused by the different rotor designand changed power sources, i.e. from DC to AC and 3-phase,—besides theelimination of brushes.

-   (i) Given that the peak current as well as voltage in AC are √2    larger than in DC for same power and torque in DC and AC, there    should be no efficiency difference on account of DC versus AC and    3-phase per se.-   (ii) In regard to rotor construction note that for 1-S-ribbon MP-A    machines only one half of the rotor body is occupied by conductors,    while the rearranged and compacted S-ribbons of MP-T machines (as in    either shapes of FIG. 5B or any other) and of AC machines with two    S-ribbons may occupy all of the rotor body, i.e. except for surface    and internal insulation layers. This is much the same as the ˜94%    rotor occupancy by conductors in the rotors of MP and MP-Plus    machines. In the former, operation with DC provides for continuous    current in the zones, accounting for about 50% of the rotor volume,    together giving rise to ˜½×94%=47% average “rotor utilization.”    Similarly, at any moment, only about 50% of the rotor body of MP-T    machines is in zones, for the same ˜½×94%=47% current utilization.    There is, then, no significant difference in regard to rotor body    conductivity between MP and MP-Plus machines over MP-T machines.    However, MP-A machines with just one S-ribbon have a rotor    utilization of only about 25%.-   (iii) Brushless MP-A and MP-T machines have an advantage over MP and    MP-Plus machines through being somewhat shorter. Their two rims add    only in the order of 4L_(m) to the machine length which will be    generally less than the width of slip rings. Previously compiled    tables covering a large range of MP-Plus machine sizes and speeds,    indicate that for otherwise same construction, the attendant ratio    of rotor lengths from substitution of slip rings for rotor rims will    be in the order of 10%. Also, the elimination of brush electrical    resistance and friction is an advantage of brushless MP-A and MP-T    machines that can significantly reduce machine losses. More    importantly yet, the extra capital investment and ownership costs of    slip rings and electrical brushes weigh against MP and MP-Plus    machines.

On balance, there is thus an expected modest advantage in power toweight ratio of brushless MP-T and 2-ribbon MP-A machines over MP-Plusmachines. This advantage is independent of expected improvements ofpower density for all MP machines through optimizing magnet arrangementsover Hallbach arrays exclusively considered up to now. Also, brushlessMP-A and MP-T machines according to the present invention are expectedto have lower capital and ownership costs.

Inertial Forces and Maximum Speeds of MP-A and MP-T Machines

The inertial forces on bearings 35 and machine axle 10, due to movingmagnet tubes 5 and 6, as compared to moving rotors 2, are approximatelyproportional to the rotating masses. Very roughly, the masses of thethree tubes at issue are similar, and thus the inertial forces andresulting stresses are roughly twice as large with moving magnet tubesthan with moving rotor. This difference will affect especially the lifetimes of low-friction bearings 35 in FIGS. 2 and 3.

The speed of simple MP and MP-Plus machines is limited by the maximumbrush sliding speed. Typically, on a sustained basis, this is about 40m/sec and could perhaps be as high as 60 m/sec. By contrast, the speedof brushless MP-A and MP-T machines is limited by the hoop stresses inthe magnet tubes that result from the centrifugal forces of the rotatingmass, i.e. magnets, flux return and structural material. The simplederivation below shows the resulting maximum rotation speeds ofbrushless MP-A and MP-T machines to be moderately higher than that dueto brush sliding speeds, as follows.

Let the diameter and average wall thickness of a magnet tube underconsideration be D and H, respectively. Further, let the minimum wallthickness of the tube, where the tensile stress on account of thecentrifugal force is largest, e.g. midway between two neighboringmagnets, be FH, with F equal to, say, F=V₂ on account of coolingchannels; and let the average mechanical density of the tube material bed=7,500 kg/m³, appropriate to high-grade permanent magnets and iron fluxreturns that also serve as the tube matrix material. Then the mosthighly tensile-stressed cross sectional area of the magnet tube, that ismost likely to fail, is

A _(C) =FH(L+4L _(m)).  (13)

Together with the correlated cross section on the opposite side of thetube 180° away, i.e. cross sectional area 2A_(C), must support thecomponent of the centrifugal force (mv²/r) of one half of the magnettube mass that is normal to them, the centrifugal force of the otherhalf representing the reaction force.

In our case r=D/2, and v is the circumferential speed v_(r), i.e.v=v_(r)=πDν according to equation 5, with ν is the rotational frequencyof the machine. Further, in view of the fact that typically L_(m)<<L,the two-part tensile-stressed cross section is

2A_(C)≈2FHL  (14)

the mass subject to the centrifugal force is

m≈½πDHL  (15)

and the normal component of the centrifugal force per unit length actingon 2A_(C) is

F _(C) =dDHv _(r) ² L/(D/2)=2dHv _(r) ² L.  (16)

Thus the resulting tensile stress on the cross sections most likely tofail is

σ_(c) =F _(C)/2A _(C) =dHv _(r) ² /FH=(d/F)v _(r) ².  (17)

Numerically, with F=½ and d=7500 kg/m³, using the mks system throughout,this yields

σ_(c)=15,000v _(r) ² [mks]  (18)

or

σ_(c)=15,000π² D ²ν² [mks].  (19)

A typical safe value for the tensile stress of the magnet tube materialis expected to be σ_(c max)=10⁸N/m²=100 MPa≈10 kgwt/mm² If so, themaximum safe speed of MP-A and MP-T machines in terms of surfacevelocity and rotation frequency is

V _(r max)≈(10⁸/15,000)^(1/2) [mks]=82 m/sec  (20)

and

ν_(r max)≈(10⁸/148,000)^(1/2) /D[mks]=26[m/sec]/D.  (21)

Thus, centrifugal forces acting on rotating magnet tubes permit highersurface speeds, namely v_(r max)≈82 m/sec, and correspondingly higherrotational frequencies of MP-A and MP-T machines, than do electricalbrushes sliding on slip rings. For example, the smallest MP-T or MP-Amachines with, say, D=0.1m rotor diameter, could operate up to 260Hz=15,600 RPM and the largest with, say, D=3 m could be run up to 8.7Hz=520 RPM. In this respect, then, MP-A and MP-T machines are superiorto MP and MP-Plus machines.

Meanwhile, however, at top rotational speed, the current frequency wouldbe

ν_(V)=N_(Z)ν_(r max).  (22)

It therefore depends on N_(Z), the number of zones per rotor, whethermachine controls based on inverters, discussed in the section MachineControls, will be adequate. If the limit should be ν_(V)=400 Hz, assuggested in that section, then the mechanically allowed top speed wouldaccording to eqs. 21 and 22 restrict N_(Z) to

N _(Zmax, νr max)=(400/26)D=16D  (23)

with D in meters. Hence it is well possible that machine controls limitthe rotation speed rather than mechanical strength of magnet tubes.MP-A and MP-T Machines with Flared Rotors and/or Without Central Axle

FIGS. 6, 7 and 8, which reproduce FIGS. 20, 21 and 22 of ref. 2,respectively, demonstrate that central axle 10 may be omitted, e.g. tolighten machines, to make them less expensive and/or to clear themachine interior for fluid flow-through, e.g. as would be particularlyappropriate when MP machines are fitted with inside propellers orimpellers 85. FIGS. 6 to 8 also demonstrate that MP rotors need not besimply cylindrical with constant rotor diameter but may comprise anyshape of flared rotor with matching magnet tubes (FIGS. 6 and 7), orbarrel-shaped rotor (FIG. 8), or indeed any rotationally symmetricalcylindrical shape.

The manufacture of any but regular simple cylindrical rotors with fittedmagnet tubes will pose a problem in MP-machine construction. Moreover,machines comprising rotors and matching magnet tubes that are not simplycylindrical or have monotonically increasing diameter in one direction,will need to be assembled in sections.

Specifically, FIGS. 6 and 7 indicate uses of MP machines with flaredrotors as pumps or fluid-driven generators by means ofpropellers/impellers 85 inside the machine body, while FIG. 8 shows howan MP machine may provide thrust through propellers 85 that extend tothe outside.

The examples of FIGS. 7 to 9 all relate to designs with stationarymagnet tubes and therefore need electrical brushes. Making such machinesbrushless will require changes corresponding to those between FIGS. 2Aand 2B. If as in FIGS. 6 to 8 axle 10 is omitted, its place may be takenby any stationary outside part that is equivalent to base plate 19 andaxle supports 23 in FIG. 2, i.e. bedrock in FIGS. 7 and 8, and thesupport from which part 25 is suspended in FIG. 9.

As is the case for all designs of MP-A and MP-T machines according tothe present invention, “axially extended” zones need not be straight andparallel to the rotation axis, even though this will be a preferredchoice. Rather, the zones may be mildly spiraled or wavy, provided onlythat the S-ribbons in the rotor are shaped to periodically substantiallyoverlap the zones, alternating with substantially overlapping the gapsbetween neighboring zones.

Possible Arrangements of the Sources of Magnetization in the MagnetTubes

As already indicated, the arrangement of the sources of magnetization inthe magnet tubes, that generate zones in the rotor is optional, asindeed is their nature. Above the discussion has centered on permanentmagnets as the sources of magnetization although it could also beelectromagnets, and among these Hallbach arrangements as in FIG. 10Ahave been the focus of attention. However, a wide range of alternativearrangements is possible of which examples are given in FIGS. 10B, 10Cand 10D, wherein 130, with a dotted pattern, is a non-magnetic materialsuch as a plastic, a rosin or a ceramic, 131, indicated by short wavylines, is a flux return material, e.g. a magnetically soft iron alloysuch as FeSi. Finally, 132, characterized by longer lines, is apermanent magnet material.

SUMMARY

Newly invented MP-A and MP-T machines generate or respond to AC or3-phase current of controllable frequency. Their otherwise insulatingrotor comprises at least one conductive “S-ribbon” with N_(S) similar,axially extended sections that in preferred positions substantiallyoverlap N_(s) neighboring “zones.” In MP-A machine rotation, this givesrise to AC electromagnetic induction and in MP-T machines to 3-phasecurrent. In “brushless” MP-A and MP-T machines, the rotor remainsstationary and the magnet tubes rotate. This permits providing rotorswith multiple terminals that may be connected to outside components suchas power supplies and/or sinks, without the need for slip rings andbrushes. The zones between any two neighboring terminals representindependent “sub-units” that may be used as motors, generators or theequivalent of transformer windings, whose voltages are proportional tothe number of zones between the terminals. The expected power density ofbrushless 2-S-ribbon MP-A machines and of MP-T machines is mildlysuperior to that of corresponding MP-Plus machines. When protected withinsulating, corrosion resistant coatings, brushless MP-A and MP-Tmachines may operate in hostile fluids, e.g. sea water.

1. An electric machine capable of operating as an electric motor, anelectric generator, or an electric transformer, comprising: multiplemagnetic field sources surrounding at the outside and inside a rotorcapable of conducting current; said rotor having a rotor wall ofsubstantially constant thickness; and said magnetic field sourcesestablishing a magnetic flux density in a multiplicity of axiallyextended, regularly spaced zones in said rotor wall; and said magneticflux density alternating in radial orientation between neighboringzones; and said rotor wall comprising at least one conductive elongatedS-ribbon; and said S-ribbon shaped so as to alternatively substantiallyoverlap a multiplicity of adjacent zones and substantially overlap thegaps between said zones when the rotor rotates relative to said magneticfield sources.
 2. An electric machine according to claim 1, wherein saidmultiple magnetic field sources are permanent magnets that are attachedto an outer magnet tube and an inner magnet tube such that theypair-wise face each other across the wall of said rotor.
 3. A machineaccording to claim 1 wherein said rotor has a predetermined rotationallysymmetrical cylindrical shape wherein lines between correlated points atthe two rotor ends may be straight or curved.
 4. An electric machineaccording to claim 2, wherein said outer magnet tube and said innermagnet tube are stationary and said rotor is rotatable.
 5. An electricmachine according to claim 2, wherein said outer magnet tube and saidinner magnet tube are rotatable and said rotor is stationary.
 6. Anelectric machine according to claim 1 wherein all surfaces of said rotorand magnet tubes are protected by means of paint, varnish, lacquer orother protective coating for use of said machine in an aggressive fluid,including for example sea water.
 7. A machine according to claim 4wherein cooling fluid is passed through channels between radial magnets.8. A machine according to claim 4 wherein at least one S-ribbon is madefrom at least one wire bundle that has been twisted and compacted.
 9. Amachine according to claim 4 wherein said rotor comprises multiple partsof S-ribbon sections of solid metal.
 10. A machine according to claim 4wherein the rotor comprises at least one joint between a rotor partcomprising S-ribbon parts composed of wires and a rotor part comprisingS-ribbon parts made of solid metal.
 11. A machine according to claim 5wherein a multiplicity of S-ribbons is subdivided into sub-units byproviding insulating barriers.
 12. A machine according to claim 11wherein sub-units are provided with plugs for connecting selectedsub-units to selected external electrical components.
 13. A machineaccording to claim 2 wherein said rotor is constituted of a set ofconcentric, mechanically fused but electrically insulated rotor layers,14. A machine according to claim 2 wherein said rotor comprises multiplelayers of wire bundles that have been twisted and compacted.